To enhance the sensitivity of a thermal-type infrared detector used for a thermal-type infrared solid-state imaging device, the structure and the manufacturing method of a thermal-type infrared solid-state imaging device capable of enhancing a fill factor described in Unexamined Japanese Patent Application KOKAI Publication No. 2001-215151 by an inventor Oda have been proposed. FIG. 4 is a sectional structural drawing along a current path showing a unit pixel of the thermal-type infrared solid-state imaging device described in the Unexamined Japanese Patent Application KOKAI Publication No. 2001-215151.
On a Si integrated circuit substrate I formed with a signal read-out circuit 27, a metal reflection film 2 is formed. For covering the metal reflection film 2, a first insulating protection film 21 is formed. Above a surface on the side of the first insulating protection film 21 of the Si integrated circuit substrate 1, a plurality of infrared receiving sections 22 (diaphragms) are disposed. Each of the infrared receiving sections 22 (diaphragms) is supported above the surface of the first insulating protection film 21 with space in between by a support section 6 across a cavity section 23. One pixel is disposed with one infrared receiving section 22 (diaphragm). The infrared receiving section 22 (diaphragm) is constituted of a bolometer thin film 13 (temperature detecting section), two electrode sections contacting the bolometer thin film 13 (temperature detecting section) of a metal wiring 15, and insulating protection films 24, 25, and 26 surrounding the bolometer thin film 13 (temperature detecting section) and the two electrode sections. The support section 6 includes a beam 6a parallel to a surface of the Si integrated circuit substrate 1 and a support leg 6b connected to one end of the beam 6a, and is structured to surround the metal wiring 15 by the insulating protection films 24, 25, and 26. The beam 6a, though depicted extremely short in FIG. 4, is actually arranged at least along one side of the infrared receiving section 22 (diaphragm) to make thermal conductance small, and its one end is connected to the infrared receiving section 22 (diaphragm). The metal wiring 15, as described above, has its one end electrically connected to the bolometer thin film 13 (temperature detecting section) as an electrode section, and has the other end electrically connected to a connection electrode 3 of the signal read-out circuit 27. An eaves section 12 is protruded from the surface opposite to the Si integrated circuit substrate 1 of the infrared receiving section 22 (diaphragm). The eaves section 12 extends in such a manner as to cover the electrode section, the support section 6, and the connection electrode 3, spaced from the electrode section inside the infrared receiving section 22 (diaphragm), the support section 6, and the connection electrode 3 of the Si integrated circuit substrate 1.
When infrared rays incident on the insulating protection films 24, 25, and 26 of the infrared receiving section 22 (diaphragm) and the eaves section 12, a part of the infrared rays is absorbed by the insulating protection films 24, 25, and 26 and the eaves section 12, respectively, and the insulating protection films 24, 25, and 26 and the eaves section 12 are heated. The infrared rays, which incident on the insulating protection films 24, 25, and 26 and the eaves section 12 but are not absorbed, pass through the infrared receiving section 22 (diaphragm), the eaves section 12, and the support section 6, respectively, and advance toward the Si integrated circuit substrate 1. The infrared rays passing through the infrared receiving section 22 (diaphragm), the eaves section 12, and the support section 6, respectively, are reflected toward the infrared receiving section 22 (diaphragm) and the eaves section 12 by the metal reflection film 2, the metal wiring 15, and the connection electrode 3, and incident on the insulating protection films 24, 25, and 26, and the eaves section 12 again. Thereby, the infrared rays reflected by the metal reflection film 2 and the like are absorbed by the insulating protection films 24, 25, and 26, and the eaves section 12, so that the insulating protection films 24, 25, and 26, and the eaves section 12 are further heated. The heat of the eaves section 12 is transmitted to the bolometer thin film 13 (temperature detecting section) through the insulating protection films 25, and 26. In this manner, the temperature of the bolometer thin film 13 (temperature detecting section) changes by the heat from the eaves section 12 and the insulating protection films 24, 25, and 26, thereby changing a resistance value of the bolometer thin film 13 (temperature detecting section). This change of the resistance value is converted into a voltage change by the signal read-out circuit 27 inside the Si integrated circuit substrate 1, and is read out as an electrical signal. Based on this electrical signal, an infrared image is formed by an external circuit.
In the present pixel structure, the eaves section 12 is protruded from the infrared receiving section 22 (diaphragm), and covers respective surfaces of the electrode section and the support section 6 opposite to the Si integrated circuit substrate 1, and the connection electrode 3 across a space. Hence, the fill factor of each pixel is increased, so that the infrared rays can be absorbed much more and the sensitivity can be enhanced.
In the technique described in the Unexamined Japanese Patent Application KOKAI Publication No. 2001-215151, all of the insulating protection film of the infrared receiving section (diaphragm), the insulating protection film of the support section, and the eaves section are formed of a silicon nitride film, a silicon oxide film or a silicon oxynitride film. Out of these films, the insulating protection film constituting the infrared receiving section (diaphragm) and the insulating protection film constituting the support section are formed by the insulating film of the same layer. However, since the eaves section is structured to extend so as to cover the electrode section, the support section, and the connection electrode, spaced from the electrode section inside the infrared receiving section, the support section, and the connection electrode of the Si integrated circuit substrate, it is formed of the insulating film of a separate layer from the infrared receiving section (diaphragm) and the support section. Hence, the eaves section is directly laminated on the infrared receiving section (diaphragm) in the manufacturing process, and an unnecessary part of the insulating film for eaves formation remains in existence, which does not contribute to the improvement of the fill factor. If this part is left intact, there arises a problem that the heat capacity of the infrared receiving section (diaphragm) meaninglessly increases, thereby causing a problem of reducing a thermal response characteristic.
To prevent the reduction of this thermal response characteristic, the unnecessary part of the insulating film for eaves formation laminated in the vicinity of the center on the infrared receiving section (diaphragm) may be partially removed by etching. Also, in the sectional structural drawing of the thermal-type infrared solid-state imaging device unit pixel shown in FIG. 4, which is described in the Unexamined Japanese Patent Application KOKAI Publication No. 2001-215151, a state in which the unnecessary part of the insulating film for eaves formation laminated on the infrared receiving section (diaphragm) is removed is depicted. According to the description of the Unexamined Japanese Patent Application KOKAI Publication No. 2001-215151, in the process of processing an insulating film for eaves formation into an eaves section form, the unnecessary part of the insulating film for eaves formation directly laminated on this infrared receiving section (diaphragm) is partially removed by etching simultaneously. In this process, since the insulating film for eaves formation has to be surely cut and divided to an eaves section for each pixel, it is necessary to sufficiently add an over-etching which implements etching thicker than the film thickness 5 of the insulating film for eaves formation. Hence, in the manufacturing method of the Unexamined Japanese Patent Application KOKAI Publication No. 2001-215151, the erasing amount of the insulating protection film constituting the infrared receiving section (diaphragm) increases. Further, because of the difficulty to control the erasing amount, there also arises a problem that variance in the characteristics among pixels, wafers, and moreover, lots increases. If the over-etching is performed extremely, there is even a risk that the insulating protection film of the infrared receiving section (diaphragm) is burst through, so that the bolometer thin film (temperature detecting section) is damaged.
To avoid such problem, the inventor of the present application and others have proposed a thermal-type infrared solid-state imaging device and the manufacturing method thereof in Unexamined Japanese Patent Application KOKAI Publication No. 2005-116856 and U.S. Pat. No. 7,276,698 B2, which are high in processing accuracy and partially remove the unnecessary part of the insulating film for eaves formation laminated on the infrared receiving section (diaphragm) while suppressing variance in the characteristics among pixels, wafers, and moreover, lots, thereby enabling the reduction of the thermal response characteristic to be suppressed. FIGS. 5 and 6 are a schematic longitudinal sectional structural drawing and a unit pixel top view showing the unit pixel of the thermal-type infrared solid-state imaging device described in U.S. Pat. No. 7,276,698 B2.
As shown in FIGS. 5 and 6, the eaves section 12 is connected to a diaphragm 5 by a ring-shaped eaves connector 18, and slightly insider thereof, an eaves opening 19 is opened. As shown in the sectional view of FIG. 5, the eaves section 12 is supported above the diaphragm 5 with space in between across from the eaves connector 18 to the eaves opening 19. The unnecessary part of the insulating film for eaves formation having been in the eaves opening 19 is removed with a sacrifice layer serving as an etching stopper provided in the center of the diaphragm 5 in an island-shape, and therefore the eaves section 12 is made to have such a cross-sectional shape. This sacrifice layer is formed simultaneously with a sacrifice layer for securing a space with the eaves section 12, the support section 6, and the like, that is, the same layer. The debris of the sacrifice layer which has become the etching stopper is removed simultaneously with the other sacrifice layers in the subsequent sacrifice layer etching process.
According to this method, the insulating film unnecessary part for eaves formation can be removed by using the etching stopper without making the manufacturing process complicated. Therefore, the problem that variance in characteristics among pixels, wafers, and moreover, lots becomes large is solved without the insulating protection film constituting the infrared receiving section (diaphragm) cut-out.